CN109565687B

CN109565687B - Enhanced uplink beam selection for massive MIMO systems

Info

Publication number: CN109565687B
Application number: CN201680088197.6A
Authority: CN
Inventors: 张翼; 缪德山; 张元涛
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2016-06-17
Filing date: 2016-06-17
Publication date: 2023-07-28
Anticipated expiration: 2036-06-17
Also published as: US11916620B2; CN109565687A; EP3473032A1; EP3473032A4; WO2017214969A1; KR102185482B1; KR20190018712A; US20190253108A1

Abstract

The wireless network transmits downlink signaling to a User Equipment (UE) that triggers an enhanced uplink beam selection protocol based on the quality of the uplink signaling of the UE that the network receives according to the basic uplink beam selection protocol. In response, the UE transmits predefined signaling, such as uplink beam reference signals (U-BRSs), with uplink beams according to the downlink signaling. The network measures and selects one or more of these uplink beams for use by the UE in transmitting uplink data and informs the UE of the selection. In various embodiments, the basic uplink beam selection protocol is based on uplink-downlink reciprocity, the downlink trigger signaling is dynamic and also selects a subset of uplink beams, and multiple UEs may be triggered in common signaling, wherein blind decoding by these UEs is enabled via scrambling IDs for the enhanced uplink beam selection protocol purpose.

Description

Enhanced uplink beam selection for massive MIMO systems

Technical Field

The described invention relates to wireless communications, and more particularly to establishing a wireless connection between a User Device (UD) and a radio access network characterized by a lack of robustness, such as that observed in line-of-sight (LOS) type radio communication characteristics. These characteristics are very common for millimeter wave (mmWave) spectrum of 5G Radio Access Technologies (RATs) being developed.

Background

Wireless radio access technologies continue to improve to handle increased data volumes and greater numbers of subscribers. The 3GPP organization is developing fifth generation (5G) wireless networks to handle peak data rates on the order of about 10Gbps (gigabits per second) while still meeting the existing ultra-low latency requirements for certain 4G applications. 5G is intended to utilize wireless spectrum in the GHz or higher order in millimeter wave (mmWave) band; and also support massive MIMO (multiple input multiple output) (m-MIMO). The M-MIMO system is characterized by a much greater number of antennas, better beamforming, and higher antenna gain than the 4G system.

One current issue within certain 3GPP teams operating on 5G systems is User Equipment (UE) side beamforming. It has not been uncommon for many years for a UE to possess multiple own antennas, but the robustness of exploiting the MIMO capability of the UE is slightly lower than that of the network side. For example, in a 4G/LTE system, a plurality of beams may be transmitted on a network side/base station side using an Active Antenna System (AAS). Based on the beamformed downlink reference signaling, the UE may make beam-specific measurements and feed back to the network the index of the downlink beam that the UE deems optimal. However, on the UE side, there are far fewer antennas (typically 2 or 4 antennas), and the small physical size of the UE actually limits the size of these several UE side antennas. However, on the UE side, a small number of antennas with size restrictions are used. For these reasons, beamforming techniques that have been developed and found to be useful on the network side are not generally considered to be deployed similarly on the UE side.

But at very high frequency bands (e.g., even above 6 GHz), the 5G system should provide a radio environment where UE-side beamforming can significantly increase the link budget. This is the field for which these teachings are directed, but the general principles are not specifically limited to 5G systems or even to GHz-level radio environments.

The following references provide some relevant background information:

● LTE: the UMTS Long Term Evolution from Theory to Practice (version 2; john Wiley & Sons, ltd.; 2011), chapter 11 and chapter 29 (last visit of 8 th month, 2016-obtainable at http:// www.aldraji.com/download/the_UMTS_Long_term_Evolding B.p df).

● Nsenga et al, "Joint Transmit and Receive Analog Beamforming in 60GHz MIMO multipath channels" published in IEEE proc.icc, 6, 2009.

● Ahmed Alkhateb et al, 10.2014, published IEEE Signal processing monograph, volume 8, volume 5, pages 831-846 at pages Channel Estimation and Hybrid Precoding for Millimeter Wave Cellular System ".

● 3GPP TS 36.213v13.1.1 (month 03 of 2016) E-UTRA Physical layer procedures, fifth section.

Disclosure of Invention

In a first embodiment of these teachings, a method is provided that includes: transmitting, to a User Equipment (UE), downlink signaling triggering an enhanced uplink beam selection protocol based on a quality of the uplink signaling received from the UE in accordance with a basic uplink beam selection protocol; receiving predefined signaling with uplink beams from the UE according to the downlink signaling; selecting one or more of the uplink beams for use by the UE in transmitting uplink data; and notifying the UE of the selection.

In a second embodiment of these teachings, a computer readable memory is provided that tangibly stores a computer program that, when executed by one or more processors, causes a host radio access node device to: transmitting, to a User Equipment (UE), downlink signaling triggering an enhanced uplink beam selection protocol based on a quality of the uplink signaling received from the UE in accordance with a basic uplink beam selection protocol; receiving predefined signaling with uplink beams from the UE according to the downlink signaling; selecting one or more of the uplink beams for use by the UE in transmitting uplink data; and notifying the UE of the selection.

In a third embodiment of these teachings, an apparatus is provided that includes at least one processor and at least one memory storing a computer program. In this embodiment, the at least one processor is configured with the at least one memory and the computer to cause the apparatus at least to: transmitting, to a User Equipment (UE), downlink signaling triggering an enhanced uplink beam selection protocol based on quality of the uplink signaling received from the UE according to a basic uplink beam selection protocol; receiving predefined signaling with uplink beams from the UE according to the downlink signaling; selecting one or more uplink beams from the uplink beams for the UE to use for transmitting uplink data; and notifying the UE of the selection.

In a fourth embodiment of these teachings, a method is provided that includes: transmitting predefined uplink signaling with uplink beams according to downlink trigger signaling in response to receiving the downlink trigger signaling; receiving an acknowledgement to the predefined uplink signaling, the acknowledgement identifying one or more of the uplink beams; and then transmitting uplink data on the identified one or more uplink beams.

In a fifth embodiment of these teachings, a computer readable memory is provided that tangibly stores a computer program that, when executed, causes a host user device to: transmitting predefined uplink signaling with uplink beams according to downlink trigger signaling in response to receiving the downlink trigger signaling; receiving an acknowledgement to the predefined uplink signaling, the acknowledgement identifying one or more of the uplink beams; and then transmitting uplink data on the identified one or more uplink beams.

In a sixth embodiment of these teachings, an apparatus is provided that includes at least one processor and at least one memory storing a computer program. In this embodiment, the at least one processor is configured with the at least one memory and the computer to cause the apparatus at least to: transmitting predefined uplink signaling with uplink beams according to downlink trigger signaling in response to receiving the downlink trigger signaling; receiving an acknowledgement to the predefined uplink signaling, the acknowledgement identifying one or more of the uplink beams; and then transmitting uplink data on the identified one or more uplink beams.

In a seventh embodiment of these teachings, an apparatus is provided, comprising: means for transmitting, means for receiving, means for selecting, and means for notifying. The means for transmitting is for transmitting downlink signaling to a User Equipment (UE) triggering an enhanced uplink beam selection protocol based on a quality of the uplink signaling received from the UE according to a basic uplink beam selection protocol. The means for receiving is for receiving predefined signaling with uplink beams from the UE according to the downlink signaling. The means for selecting is for selecting one or more of the uplink beams for use by the UE for transmitting uplink data, and the means for notifying is for notifying the UE of the selection. In certain non-limiting embodiments, the means for transmitting and the means for receiving comprise respective transmitters and receivers of a radio, in combination with one or more memories and enabling software stored on a local memory; the means for selecting comprises one or more processors having software and memory, and the means for notifying comprises a transmitter.

In an eighth embodiment of these teachings, an apparatus is provided, comprising: means for transmitting, means for receiving and means for transmitting. The means for transmitting is for transmitting predefined uplink signaling with uplink beams according to downlink trigger signaling in response to receiving the downlink trigger signaling. The means for receiving is for receiving an acknowledgement to the predefined uplink signaling, the acknowledgement identifying one or more of the uplink beams. The means for transmitting is for transmitting uplink data on the identified one or more uplink beams after receiving the acknowledgement. In certain non-limiting embodiments, the means for transmitting and the means for transmitting comprise a transmitter of a radio in combination with one or more memories and enabling software stored on the local memory, and the means for receiving comprises a receiver of the radio and one or more processors with the software and the memory.

These and other aspects are described in further particular detail below.

Drawings

Fig. 1 is a conceptual diagram illustrating uplink and downlink beams in a particular radio environment in which embodiments of these teachings may be deployed to increase link budget.

Fig. 2 is a conceptual diagram illustrating uplink and downlink beams in a different radio environment than that of fig. 1 in which embodiments of these teachings may also be deployed to advantage.

Fig. 3 is a signaling diagram between a base station and a user equipment illustrating an embodiment of the disclosed beam selection mechanism deployed for use when a reciprocity-based mechanism does not find a suitable uplink beam.

Fig. 4A is a table illustrating mapping of uplink beam reference signals (U-BRSs) to different combinations of resource blocks and OFDM symbols according to one specific non-limiting example.

Fig. 4B illustrates 8 possible spatial beams and subsets thereof for a UE that may be identified when triggering the enhanced uplink beam selection protocol shown in fig. 3, according to one particular embodiment.

Fig. 5A-5B are process flow diagrams summarizing certain aspects of the present invention from the perspective of a network radio access node and user equipment, respectively.

Fig. 6 is a schematic diagram illustrating some components of a radio network access node and a UE, each suitable for practicing various aspects of the present invention.

Detailed Description

Example embodiments of these teachings provide a fast and accurate uplink beam selection scheme. As will be described further below, in one embodiment, the UE transmits an uplink beam reference signal (U-BRS) after being triggered by the network to transmit the uplink beam reference signal (U-BRS). The U-BSRS assists the network in selecting uplink beams, for example, when conventional uplink beam selection techniques (such as uplink beam selection techniques based on reciprocity with the selected downlink beam) are inadequate. This enables the network to make enhanced beam selection based on the measurements of the U-BSRS that it triggers the UE to transmit. Example trigger and signaling mechanisms are discussed in detail below.

In general, the following discussion assumes that the uplink data is selected for the purpose of transmitting data, as this is typically the case when the maximum increase in overall link budget will become apparent, but these techniques may also be used to select a beam for transmitting control information from the UE to the network. In practice, the uplink beam intended to be used for the control channel will only multiplex the uplink beam selected for transmitting data. Further, while some of the examples below are in the context of selecting one uplink beam, these same techniques may be used to select two or more uplink beams from a larger set of all possible uplink beams that a given UE is capable of transmitting.

For background purposes, the concept of reciprocity for selecting uplink beams is briefly outlined. In the downlink direction, it is known to use beam-specific reference signals in the process of selecting the appropriate downlink beam. For example, the downlink quality of the different beams may be measured using channel state information reference signals (CSI-RS) or Secondary Synchronization Signals (SSS), and one or more downlink beams may be selected by comparing these measurements to each other and/or to some threshold. The concept of beam reciprocity assumes that the similarity between downlink and uplink channels is sufficiently common that a downlink beam from which a UE receives its downlink data from the network can be used as a basis for selecting an uplink beam for transmitting uplink data. Because the downlink beam is selected based on some qualitative and quantitative basis (such as the CSI-RS or SSS examples described above), the assumed correspondence between uplink and downlink extends the downlink analysis to be equally valid for the downlink as well.

However, this assumption of the correspondence of the uplink and the downlink may be ineffective in some scenarios. Fig. 1 illustrates an embodiment whose salient point is the use of different downlink transmission powers for different transmission points. The example of fig. 1 has a macro eNB transmitting downlink data to a UE, but the same UE transmits its uplink data to an associated micro/pico eNB. The radio environment of fig. 1 is becoming more and more common in LTE-a deployments where a macro eNB and a micro/pico eNB operate in a coordinated manner such that all data to and from a UE is routed through the macro eNB, the macro eNB having a network interface with the micro/pico eNB and connecting the micro/pico eNB to a core network via the network interface. In the radio environment of fig. 1, the downlink and uplink differ significantly in both transmit power and distance between the transmitter and receiver. Obviously, for beam selection purposes, the downlink channel from the macro eNB will reasonably reflect the assumption that the uplink channel to the micro/pico eNB is not valid.

Fig. 2 illustrates different radio environments in which link budgets may be improved by deploying embodiments of these teachings. In fig. 2, from the perspective of the UE, the transmission beam and the reception beam change due to the movement of the UE even though the change is as small as the change in the posture or hand position of the person holding (holding) the UE. As shown, the transmit/receive beam at the 12 o 'clock position of the UE is typically aligned with the base station in the illustrated UE TX/RX (transmitter/receiver) beam 2 position, but the same 12 o' clock beam is not located in another UE TX/RX beam 1 position. In this case, at any given moment, the downlink beam may be a suitable proxy for selecting the uplink beam, but the movement of the UE makes this downlink beam selection valid only before the UE moves again.

As a further consideration, the radio signal propagation characteristics in the 5G mmWave frequency region are quite different from more conventional cellular frequencies. Specifically, for 5G mmWave frequencies, the reflectivity is small, and the radio link is subject to environmental interference to the extent that the radio link can be considered to be limited to line of sight. As such, 5G systems are being developed to deploy a large number of radio Access Points (APs), with UEs having connections with the AP cluster at any given time. Slightly changing the location of the UE may hide the antenna of the handset from its line-of-sight link with one network access node/AP and force the UE to activate its connection with another node/AP in the cluster. This environment is similar to that of fig. 2, but where the UE's connections to the two illustrated locations are for different APs.

The radio environment is not the only problem with proper beam selection. The beam change scenario differs for different UEs from different manufacturers or from different models of the same manufacturer in that: different UE models may be easier or less likely to break the minimum bit/block error rate due to poor beam selection than their counterparts. As can be seen from all these examples, it is difficult to develop only the downlink reference signals to keep up with the changes in uplink beams for all UEs and all different radio environments, especially when considering the practical limitations on the signaling overhead associated with transmitting downlink reference signals and reporting uplink measurements.

Embodiments of these teachings may be deployed as a stand-alone uplink beam selection protocol. However, in the following examples, the uplink beam selection protocol is interpreted as a complement to the more conventional reciprocity technique for selecting uplink beams, which will be deployed in environments where it is determined that a separate reciprocity uplink beam selection technique is unsuitable. Whether independent or in addition to other uplink beam selection techniques, these teachings provide a technique for selecting one or more uplink beams on which to transmit data of a UE that is both fast and accurate.

Fig. 3 illustrates signaling between a base station and a UE according to such an example. Steps 1 to 5 represent a basic uplink beam selection protocol 310, while steps 6 to 9 represent an enhanced uplink beam selection protocol 320 according to these teachings. In this example, the basic uplink beam selection protocol 310 is a reciprocity technique for selecting an uplink beam based on quantitatively and qualitatively selected downlink beams, but this is not a limitation on what may be used as the basic uplink beam selection protocol 310, and other known or yet to be developed techniques may be used instead.

Further, although fig. 3 is in the context of a single base station, that does not mean a single transmission point; the base station may transmit or control transmissions from a plurality of physically distinct transmission points, each of which may each define one or more transmission beams, such as a remote radio head, micro/pico eNB, AP, etc. These different transmission points may each define (with the associated UE) at least one or more downlink beams, but depending on the radio environment, these different transmission points may or may not define with the UE one or more uplink beams; referring to fig. 1, an example of such a downlink/uplink difference.

At step 1 of fig. 3, a base station transmits downlink beam specific reference signals to a UE on a plurality of downlink beams; at step 2, the UE receives the downlink beam-specific reference signal. At step 3, the UE measures these, e.g., reference signal received power RSRP and/or reference signal received quality RSRQ, and reports these measurements to the base station. The measurement result indicates the channel quality of the combination of the transmission beam at the base station side and the reception beam at the UE side. At step 4, the base station evaluates the reported measurements, selects which downlink beam or beams to use with the UE, and informs the UE of the selection of downlink beams for the network. The downlink beam or beams include a transmission beam or beams at the base station side and a reception beam or beams at the UE side. With the downlink beam selection, at step 5, the UE selects a corresponding uplink beam and transmits its next data amount to the base station on the selected uplink beam or beams.

In some variations of this basic beam selection protocol 310, the UE evaluates its measurements and makes downlink beam selection itself at step 3. While this shifts the processing burden to the UE, the signaling overhead is reduced by allowing the UE to signal only the index of the downlink beam selected at its step 3, rather than its actual beam measurement. This also reduces overhead signaling at step 4, since the UE does not need to be informed of downlink beam selection. Regardless, for reciprocal beam selection techniques in general, the uplink beam is selected to correspond to the analytically selected downlink beam, so, for example, if beam index #3 is selected as the downlink beam at step 4 (or if the UE itself is selected at step 3), beam index #3 will be used for uplink data transmission at step 5. Typically, both the base station and the UE use the same uplink beam selection algorithm, so when beam reciprocity techniques are used, it is not necessary to signal which is the uplink beam.

Now, at step 6 of fig. 3, the base station determines that the link quality is poor and in response triggers the enhanced uplink beam selection protocol 320. A specific example of how the UE may be signaled to the network/base station to trigger the protocol 320 will be described in further detail below with reference to the specific example in fig. 4B.

Although the network may determine that the link quality is not good at step 6 by several options, this determination means that the uplink beam selected according to the basic uplink beam selection protocol 310 is not suitable anymore or is no longer as suitable as originally. It is possible that the difference between downlink and uplink is so great that reciprocity does not select the appropriate uplink beam at all, in which case step 6 will be performed immediately after the UE has transmitted its first lot of data on the uplink beam that was put into use during this step of the base protocol 310 at step 5. Alternatively, it is possible that the uplink beam is suitable for a period of time but has degraded afterwards.

The beam-specific reference signals transmitted by the network at step 1 are typically static and thus if the base station perceives degradation on the downlink corresponding to degradation on the uplink (e.g., a greater number of negative acknowledgements from the UE), the base station may choose to re-run the base protocol 310 once the next batch of CSI-RSs is scheduled for transmission (CSI-RSs in LTE are periodically sparsely transmitted from each physical and virtual antenna port) or based on SSS measurements are triggered to report. In either of these cases, the base station attempts to re-evaluate the choice of downlink beam selection and the base protocol 310 for reciprocity may discover the new uplink beam to attempt.

However, in response to perceived degradation in the uplink, the base station may in turn choose to operate the enhanced uplink beam selection protocol 320 as depicted in fig. 3. In one example, this may be due to a delay until the next scheduled CSI-RS transmission by the base station, in which case the base station may choose to trigger the enhanced protocol 320 even if there is degradation in the downlink corresponding to degradation in the uplink. In another example, the base station may perceive degradation in the uplink but no degradation in the downlink, meaning that the selected downlink beam is not or no longer a suitable agent for selecting an uplink beam.

The base station may use a variety of measurements to determine that the link quality is poor at step 6. Many measurements are well established in the wireless field, for example: bit or block error rate (BER or BLER), relative Signal Strength (RSSI), signal to interference plus noise ratio (SINR), and Channel State (CSI) may all be used to measure the quality of the uplink and thereby determine whether the uplink has degraded to the point that the base station should invoke the enhancement protocol 320.

Whichever specific measurement metric or metrics are used for uplink evaluation at step 6, this determination can be viewed in a number of ways for the particular uplink beam in use. For example, if we consider the uplink beam selected by the base protocol 310 as the 'selected beam' evaluated for quality at step 6, the base station may determine that the link is bad enough to trigger the enhancement protocol 320 if one or more of the following criteria are true, where in this case the candidate beam is any other uplink beam that the UE may be able to use:

● Link quality for the selected beam is below a threshold;

● The link quality of the other candidate beam is above a threshold;

● The link quality difference between the selected beam and the candidate beam is less than a threshold;

● The link quality difference between the selected beam and the candidate beam is less than an offset threshold, wherein the offset is determined based on the transmit power of the base station.

After making this determination, the base station completes step 6 of fig. 3 by sending a trigger bit (or one bit) to the UE to invoke the enhanced uplink beam selection protocol 320. Once triggered, the UE transmits an uplink beam selection reference signal (U-BRS) on one or more beams at step 7, which the network then measures and evaluates at step 8. Based on the measurements and evaluations, the network/base station selects an uplink beam and informs the UE of its choice via wireless signaling. In this regard, the U-BRS according to these teachings is transmitted to assist the network in selecting an uplink beam. Fig. 3 ends with step 9, at step 9, the UE transmits data to the network/base station on the selected beam (or beams) notified at step 8 and selected by the base station according to the enhanced uplink beam selection protocol 320.

Fig. 4A is a table of radio frequencies (as physical resource blocks PRBs) versus OFDM symbols and gives an example for U-BRS transmission for a UE with 16 candidate beams and 4 transmit-receive units (TXRUs). The resource elements within 4 PRBs and 4 OFDM symbols are used for U-BRS transmission for the UE. Preferably, the U-BRSs for the different beams are transmitted in orthogonal resources to better ensure measurement accuracy at the base station side. U-BRS transmissions for different UEs may be multiplexed by Code Division Multiplexing (CDM) (e.g., by shifting of a cyclic base sequence). Fig. 4A is merely an example, and there are a variety of other resource mappings and multiplexes for U-BRSs that may be used to deploy embodiments of these teachings. As will be seen in the example of fig. 4B below, in some examples, a UE may transmit a U-BRS on fewer than all of its possible beams for some embodiments.

In order to obtain fast uplink beam selection, dynamic trigger signaling may be used. That is, the trigger signaling at step 6 of fig. 3 may be on an as needed basis, as opposed to regular and static conventional CSI-RS on the downlink. In the following, it is assumed that the 8 beams shown for the UE in fig. 4B represent all possible UE beams for uplink data, but of course, the beams constituting all possible uplink beams of the UE may be different for other UEs. The network may learn this information from the UE type or class, which will inform the network about the total number of transmit antennas for a particular UE. For the purposes of fig. 4, the beam of the UE that transmits its U-BRS after being triggered to transmit its U-BRS is considered a candidate beam.

In one example, it is possible that the network would like the UE to transmit its U-BRS on all of its possible beams. When all candidate beams are needed for measurement, the network may use 1-bit trigger signaling at step 6 of fig. 3. 1-bit trigger signaling may also be used where embodiments of these teachings do not employ the beam subset illustrated in detail by way of example in fig. 4B; in this case, the enhanced uplink beam selection protocol 320 is invoked at any time, the network will trigger the UE with 1-bit signaling, and the UE will respond by transmitting its U-BRS on all its possible uplink beams.

Fig. 4B details a more compact solution compared to the 1-bit signaling described above, reducing the overhead of the U-BRS and the delay of beam selection of the network by limiting the number of candidate beams for which the UE transmits the U-BRS. In this embodiment, all possible uplink beams of the UE are divided into two or more subsets, and only the beams in the selected subset are used by the UE to transmit its U-BRS. The subset will then present all candidate beams for measurement by the network and will not transmit U-BRSs associated with beams that are not in the selected subset. For this embodiment, there may be more trigger bits; for the example in fig. 4B where there are three different subsets, at least two bits may be used for the dual purpose of triggering the enhancement protocol 320 and indicating which subset of beams to select.

Table 1 below presents one example of two trigger bits for the three subsets defined in fig. 4B. The values of these two bits may be regarded as indexes in this table, which are predefined for the base station and the UE and stored in the respective local memories of the base station and the UE before any trigger bits are sent at step 6 of fig. 3.

Table 1: example trigger bit values for transmitting different subsets of uplink beams of a U-BRS

Alternatively, the value '00' may indicate the selection of all possible beams, as shown in table 2 below. In other embodiments, there may be a greater number of subsets and a corresponding greater number of trigger bits; and in other embodiments some trigger bits may select multiple otherwise defined subsets (e.g., bit values 000 and 001 are first and second subsets, respectively, and bit value 011 selects both the first and second subsets). Although any given beam may be listed in more than one subset, each subset is unique to each other subset, and each subset includes fewer than all possible beams for the UE, with the possible exception of one subset. The division of the beam into subsets may be flexible, e.g., the base station may send an index for each subset to the UE through higher layer signaling (e.g., radio resource control signaling). Alternatively, in another deployment, the subset may be fixed and predefined with published standards for a given radio access technology.

Table 2: example trigger bit values for transmitting different subsets of uplink beams of a U-BRS

Whether flexibly defined or fixed, it is advantageous to construct the subsets as follows. First, to ensure robustness of beam selection, at least one beam subset should comprise a plurality of orthogonal beams with a large beam spacing between them. Another alternative is that one beam subset should include all possible uplink beams. The beam subset #1 of fig. 4B is triggered by signaling bit '01' in the table above and represents such a subset: each beam is orthogonal to each other beam, and two beams in the subset are not spatially adjacent. Second, the beams in the other subsets may be contiguous with a small spatial separation between them. The beam subsets #2 and #3 triggered by the corresponding signaling bits '01' and '11' in the table above in fig. 4B reflect the following principle: in a given subset, each beam is spatially adjacent to another beam such that all beams in the subset form a spatially contiguous beam set.

As wireless networks become more and more complex, as shown in the signaling diagram of fig. 3, it is no longer sufficient to assume a single transmission point, and in particular the 5G mmWave radio access technology for AP clusters with serving given UEs as described above. In this regard, for each spatially distinct transmission point where the UE has an uplink connection, in one embodiment, there may be a single invocation of the enhanced protocol 320 and a single subset triggered for the UE, and all associated transmission points may make their measurements starting with the UE's transmission of U-BRSs on the beams of that single subset, and then coordinate between them which beam or beams to select for uplink before signaling to the UE at step 8 of fig. 3.

In another embodiment, the UE unilaterally determines to invoke or not invoke the enhancement protocol 320 for each spatially distinct transmission point of the uplink connection and triggers the UE and identifies the subset of beams regardless of other transmission points. In this case, the UE will transmit on all beams currently selected by any of a variety of different transmission points.

To explain the details below more simply, assume again a single transmission point, when a UE transmits its U-BRSs on the beam indicated by the trigger signaling, the base station will receive these U-BRSs on all beams (all possible UE beams or identified subsets) selected by the trigger signaling. Since some receive beams are not available for data transmission by other UEs, the uplink transmission of the U-BRS will have an impact on the network's reception of uplink transmissions from other UEs. Further considering that there is more than one UE in a cell that may need to transmit a U-BRS, it is clear that once the above teachings are widely adopted, this problem is not an occasional problem. To solve this interference problem, U-BRSs from different UEs may be aggregated in time by multiplexing them all into one specific radio subframe.

Then, common trigger signaling would be a natural choice due to multiplexing of data transmissions with other UEs. The dynamic signaling format may refer to DCI format 3/3A. However, a new scrambling ID for scrambling is needed, e.g. an uplink beam quality measurement scrambling ID used for blind decoding by the UE. In this example, the trigger bits for all UEs triggered to transmit a U-BRS are scrambled with the corresponding uplink beam quality measurement scrambling ID and then multiplexed into one DCI format 3 and/or 3A, which DCI format 3 and/or 3A itself is scrambled with a Radio Network Temporary Identifier (RNTI) and transmitted on the downlink, where the RNTI is specific to the new uplink beam selection function. The target UE can decode the DCI using this RNTI and may then blind decode its particular trigger bits by using the scrambling IDs previously assigned to them alone. The specific locations (location indices) of the trigger bits multiplexed within the DCI for any given UE may be pre-arranged with the network via RRC signaling, so the UE need not attempt to decode all trigger bits multiplexed into the DCI for all UEs.

Embodiments of these teachings provide certain technical advantages over the state of the art. In particular, the transmission of uplink beam-specific reference signals may be dynamically triggered, which is particularly advantageous when used to enhance uplink beam selection that may have been made using reciprocity. Another advantage is that multiple bits may be used to dynamically trigger enhanced uplink beam selection simultaneously, as well as to select a specific subset of UE beams. This advantage is enhanced by using the above-described guidance for defining subsets, i.e. multiple orthogonal beams with a larger beam spacing for one subset to support robust beam selection. Additionally, trigger signaling for transmitting the U-BRS may be done on a group basis in a subframe to limit the impact of U-BRS transmissions on data transmissions by other UEs. Also, a new scrambling ID, such as an uplink beam quality measurement scrambling ID, may be used for the group trigger signaling described above.

Fig. 5A is a flow chart summarizing some of the above-described features for how a network performs its uplink beam selection based on a triggered U-BRS from the perspective of the network (more specifically, from the perspective of a network radio access node such as a base station in the above-described example).

Block 502 mentions a basic Uplink (UL) beam selection protocol, one example of which is shown in fig. 3, but is not repeated in fig. 5A. Briefly, in accordance with the fig. 3 example of the reciprocal basic beam selection protocol 310, a base station transmits beam-specific reference signals (such as, for example, beam-specific discovery signals) for UE measurements on the downlink uplink with transmit and receive beamforming. Then, the base station selects a transmission beam for itself and a reception beam for the UE, and notifies the beam selection result. If the notification is explicit, one way to do this is to have the base station indicate the transmit and receive beam indices directly to the UE. If the notification is implicit, one way to do this is to indicate the selected link index to the UE, which the UE uses in reporting its measurement results, so there is no ambiguity between the base station and the UE.

Whether or not the uplink beam selection is substantially reciprocal, block 502 reflects that at some point, the network sends Downlink (DL) signaling to the UE that triggers the enhanced UL beam selection protocol based on the quality of the uplink signaling received by the network from the UE. The uplink signaling at block 502 is received over the network on an uplink beam selected by the basic uplink beam selection protocol, which block 502 designates the uplink signaling as received according to the basic UL beam selection protocol.

The downlink signaling of block 502 is the trigger signaling mentioned above, which may also select a predefined subset of UE beams in some embodiments. In some embodiments, the base station may utilize common dynamic signaling to trigger uplink beam selection reference signals based on some criteria, such as uplink quality comparison as described above with some threshold or some other example of candidate uplink beams. For the case of common dynamic signaling, the common trigger signaling is shared by many UEs. The mechanism for group signaling may be considered somewhat similar to signaling group transmit power control, but in one embodiment the common dynamic signaling used to trigger the UE to send the U-BRS is downlink control format DCI3 or DCI3A but with a different scrambling ID. To distinguish from other scrambling IDs, these scrambling IDs may be regarded as uplink beam quality measurement scrambling IDs (ubqm_scid) and each UE is assigned one scrambling ID, so that the UE may blindly decode DCI3/3A, and any UE that is able to decode DCI3/3A with its assigned ubqm_scid means that the UE is triggered to transmit a U-BRS. The actual trigger bits may be a single bit or may be more than one bit that also selects a subset of beams, as shown in the examples above.

Further, in fig. 5A, at block 504, the base station receives predefined signaling with uplink beams from the UE according to DL signaling. In the above example, the predefined signaling is a U-BRS that is sent on the uplink beam according to the trigger bits (where a single bit embodiment selects all possible beams of the UE). At block 506, the base station selects an uplink beam or more generally one or more of the uplink beams received at block 504, and the selection is based on measurements obtained by measuring and evaluating the predefined signaling received at block 504. Finally, at block 508, the base station informs the UE of its beam selection results, such as by adding the new information to any of various conventional control signaling messages.

Fig. 5B is a flow chart outlining certain aspects of the present invention from the perspective of a UE on how to perform some of the above-described features of the portion of the enhanced uplink beam selection protocol 320. The basic uplink beam selection protocol 310 is not shown in fig. 5B, which basic uplink beam selection protocol 310 may be used prior to the enhancement protocol 320 in some deployments of these teachings. For the reciprocity-based basic protocol type, the UE will receive and measure downlink beam-specific reference signals, if beam selection is done on the UE side, the UE reports the beam index; or if beam selection is done at the network side, the UE reports its measurement results, such as RSRP/RSRQ. Each beam measurement has an index and is associated with one transmit beam and one receive beam. If the enhanced protocol 320 is not triggered (or before any such trigger), the UE will make its uplink transmission based on the uplink beam selected by reciprocity. This means that the downlink receive beam of the UE is used as the uplink transmit beam of the UE.

Whether or not such a base protocol is used, fig. 5B begins at block 552 with downlink trigger signaling for enhanced uplink beam selection protocol; in response to receiving the trigger signaling, the UE transmits predefined uplink signaling with uplink beams according to the downlink trigger signaling. If the trigger signaling is only one bit and triggers the UE, the trigger is transmitted on all uplink beams of the UE and thus the uplink beams are multiple uplink beams according to the downlink trigger signaling. Conversely, if the trigger signaling selects a table index identifying a subset of beams as detailed above, the beams in the identified subset constitute a plurality of uplink beams. Regardless, it is only on the beams associated with the downlink trigger signaling on which the UE is transmitting, and in the above example, the predefined signaling transmitted on these beams is a U-BRS. This will assist the network in selecting an uplink beam for the UE.

In one embodiment, the UE transmits its uplink beam selection reference signal at block 552 when the UE detects common trigger signaling, which may be decoded using the scrambling codes detailed above. Due to processing delays at the UE, uplink transmissions of the U-BRS on multiple uplink beams may begin after the UE has received the trigger signaling over several subframes (e.g., four subframes).

At block 554, the UE receives an acknowledgement to the predefined signaling of block 552, and the acknowledgement identifies one or more of the uplink beams used for the predefined signaling in block 552. Finally, at block 556, the UE transmits uplink data according to the uplink beam selection result of the network, which identifies one or more beams at block 554.

Among the technical effects of these teachings, the uplink beam selection mechanism described herein is fast and accurate, the beam switching mechanism is robust, and by selecting a more appropriate uplink beam than that accomplished by the reciprocity-based selection method, transmission reliability and system capacity are expected to be improved. The signaling overhead for achieving these advantages is considered to be easily within the more efficient link budget.

Each of fig. 5A-5B may itself be considered an algorithm and more generally represent steps of a method and/or certain code segments of software stored on a computer readable memory or memory device embodying the respective fig. 5A-5B algorithm for implementing these teachings from the perspective of the respective device (base station or similar radio network access node, or UE). In this regard, the present invention may be embodied as a machine-readable non-transitory program storage device, such as, for example, one or more processors of a radio network access node or UE, tangibly embodying a program of instructions executable by the machine for performing operations, such as those shown in fig. 5A-5B and described in detail above.

Fig. 6 is a high-level diagram illustrating some of the relevant components of various communication entities that may implement various parts of these teachings, including a base station, typically identified as a radio network access node 20, a Mobility Management Entity (MME), which may also be co-located with a user plane gateway (uGW) 40, and a User Equipment (UE) 10. In the wireless system 630 of fig. 6, the communication network 635 is adapted to communicate with devices such as mobile communication equipment (which may also be referred to as UE 10) via the radio network access node 20 over a wireless link 632. Network 635 may include an MME/serving GW 40 that provides connectivity to other and/or wider networks (e.g., internet 638) such as public switched telephone networks and/or data communication networks.

The UE 10 includes a controller, such as a computer or a Data Processor (DP) 614 or a plurality thereof, a computer readable memory medium, such as a Radio Frequency (RF) transceiver or more generally a radio 612, embodied as a memory (MEM) 616 (or more generally a non-transitory program storage device) that stores a program of computer instructions (PROG) 618, and a suitable wireless interface, such as a Radio Frequency (RF) transceiver or more generally a radio 612, for bi-directional wireless communication with the radio network access node 20 via one or more antennas. In general, the UE 10 may be considered a machine that reads the MEM/non-transitory program storage device and executes computer program code or an instruction executable program stored on the MEM/non-transitory program storage device. Although each entity of fig. 6 is shown as having one MEM, in practice each entity may have multiple discrete memory devices, and the associated algorithm(s) and executable instructions/program code may be stored on one or several such memories.

In general, various embodiments of the UE 10 may include, but are not limited to: mobile user equipment, cellular telephones, smartphones, wireless terminals, personal Digital Assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, internet appliances permitting wireless internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

The radio network access node 20 also includes a controller, such as a computer or Data Processor (DP) 624 or a plurality thereof, a computer readable memory medium embodying a memory (MEM) 626 storing a program of computer instructions (PROG) 628, and a suitable wireless interface, such as an RF transceiver or radio 622, for communicating with the UE 10 via one or more antennas. The radio network access node 20 is coupled to the MME 40 via a data/control path 634. Path 634 may be implemented as an S1 interface. The radio network access node 20 may also be coupled to other radio network access nodes via a data/control path 636, which path 636 may be implemented as an X5 interface.

MME 640 includes a controller, such as a computer or Data Processor (DP) 644 or a plurality thereof, a computer readable memory medium that stores a program of computer instructions (PROG) 648 that is embodied as a memory (MEM) 646.

At least one of the PROGs 618, 628 is assumed to include program instructions that, when executed by the associated one or more DPs, enable the device to operate in accordance with exemplary embodiments of this invention. That is, various exemplary embodiments of this invention may be implemented at least in part by computer software executable by DP 614 of UE 10, and/or by DP 624 of radio network access node 20, and/or by hardware, and/or by a combination of software and hardware (and firmware).

For the purposes of describing various exemplary embodiments in accordance with this invention, the UE 10 and the radio network access node 20 may also include dedicated processors 615 and 625, respectively.

The computer-readable MEMs 616, 626, and 646 may be any type of memory device suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The DPs 614, 624, and 644 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital Signal Processors (DSPs), and processors based on a multi-core processor architecture, as non-limiting examples. The wireless interface (e.g., RF transceivers 612 and 622) may be of any type suitable to the local technical environment and may be implemented using any suitable communication technology such as an individual transmitter, receiver, transceiver, or combination of these components.

The computer readable medium may be a computer readable signal medium or a non-transitory computer readable storage medium/memory. The non-transitory computer-readable storage medium/memory does not include a propagated signal and may be, for example, but is not limited to: an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. Since a propagation medium such as a carrier wave is memory-less, the computer readable memory is non-transitory. More specific examples (a non-exhaustive list) of the computer-readable storage medium/memory would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

It should be understood that the foregoing description is only illustrative. Various alternatives and modifications can be devised by those skilled in the art. For example, the features recited in the various dependent claims may be combined with each other in any suitable combination(s). In addition, features from the different embodiments described above may be selectively combined into new embodiments. Accordingly, the description is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

The communication system and/or network nodes/base stations may include network nodes, or other network elements implemented as servers, hosts, or nodes operatively coupled to the remote radio heads. At least some of the core functions may be implemented as software running in a server (which may be in the cloud) and implemented with network node functions in a manner as similar as possible (taking into account delay constraints). This is known as network virtualization. The "work allocation" may be based on a division of operations that may run in the cloud and operations that must run nearby in order to delay a requirement. In a macrocell/small cell network, the "work allocation" between macrocell nodes and small cell nodes may also be different. Network virtualization may include the process of combining hardware and element network resources and network functions into a single software-based management entity virtual network. Network virtualization may involve platform virtualization, typically in combination with resource virtualization. Network virtualization can be categorized as: many networks or portions of networks are combined externally into virtual units or internally provide network-like functionality for software containers on a single system.

The following are some acronyms used herein:

BS (eNB for enhanced nodeB)

DCI dynamic control information

DL downlink

CSI channel state information

MME mobility management entity

m-MIMO massive multiple input multiple output

mmWave millimeter wave

RRC radio resource control

RS reference signal

RSRP reference signal received power

RSRQ reference signal reception quality

SINR signal-to-dry ratio

TP transmission point

UE user equipment

uGW user plane gateway

U-BRS uplink beam reference signal

UL uplink

Claims

1. A method for communication, comprising:

invoking sending downlink trigger signaling to a user equipment, the downlink trigger signaling indicating a set of uplink beams;

receiving predefined uplink signaling using the uplink beam indicated by the downlink trigger signaling;

transmitting an acknowledgement to the predefined uplink signaling, wherein the acknowledgement identifies one or more of the uplink beams for use by the user equipment to transmit uplink data; and

the uplink data is received on the identified one or more of the uplink beams.

2. The method according to claim 1, comprising: the downlink trigger signaling is transmitted after receiving uplink data from the user equipment according to a basic uplink beam selection protocol, the basic uplink beam selection protocol comprising reciprocity, wherein a user equipment beam for uplink data is selected based on a network beam for downlink data.

3. The method of claim 1, wherein the downlink trigger signaling selects one or more subsets from at least two predefined subsets of all possible user equipment uplink beams.

4. A method according to claim 3, wherein:

at least one of the predefined subsets defines a plurality of orthogonal beams; and

at least another one of the predefined subsets defines a plurality of spatially adjacent beams.

5. The method of claim 1, wherein the downlink trigger signaling is scrambled with a scrambling identity to enable the user equipment to blindly decode the downlink trigger signaling using the scrambling identity.

6. The method of any of claims 1-5, wherein the predefined uplink signaling comprises uplink beam-reference signals.

7. The method according to any of claims 1 to 5, wherein the predefined uplink signaling is sent in predefined subframes and multiplexed with predefined uplink signaling from a plurality of other user equipments that are similarly triggered to send respective predefined uplink signaling.

8. The method according to any of claims 1 to 5, wherein the method is performed by a network radio access node operating with a 5G mmWave radio access technology.

9. A computer readable storage medium having stored thereon program code configured to, when executed, cause a host network radio access node to perform the method of any of claims 1 to 5.

10. An apparatus for communication, comprising:

at least one processor and at least one memory storing a computer program, wherein the at least one processor is configured with the at least one memory and the computer program to cause the apparatus at least to:

the uplink data is received on the identified one or more of the uplink beams.

11. The apparatus of claim 10, wherein the at least one processor is configured with the at least one memory and the computer program to cause the apparatus to: the downlink trigger signaling is transmitted after receiving uplink data from the user equipment according to a basic uplink beam selection protocol, the basic uplink beam selection protocol comprising reciprocity, wherein a user equipment beam for uplink data is selected based on a network beam for downlink data.

12. The apparatus of claim 10, wherein the downlink trigger signaling selects one or more subsets from at least two predefined subsets of all possible user equipment uplink beams.

13. The apparatus of claim 12, wherein:

14. The apparatus of claim 10, wherein the downlink trigger signaling is scrambled with a scrambling identity to enable the user equipment to blindly decode the downlink trigger signaling using the scrambling identity.

15. The apparatus according to any of claims 10 to 14, wherein the predefined uplink signaling comprises uplink beam-reference signals.

16. The apparatus according to any of claims 10 to 14, wherein the predefined uplink signaling is sent in predefined subframes and multiplexed with predefined uplink signaling from a plurality of other user equipments that are similarly triggered to send corresponding predefined uplink signaling in predefined subframes.

17. The apparatus according to any of claims 10 to 14, wherein the apparatus is a network radio access node or a component thereof operating with a 5G mmWave radio access technology.

18. A method for communication, comprising:

transmitting predefined uplink signaling with a set of uplink beams indicated by downlink trigger signaling in response to receiving the downlink trigger signaling invoked from the base station;

receiving an acknowledgement to the predefined uplink signaling, wherein the acknowledgement identifies one or more of the uplink beams; and

uplink data is transmitted on the identified one or more of the uplink beams.

19. The method of claim 18, wherein the downlink trigger signaling is received after transmitting uplink data selected according to a basic uplink beam selection protocol comprising reciprocity, wherein a beam of a user equipment for uplink data is selected based on a beam of a network for downlink data.

20. The method of claim 18, wherein the downlink trigger signaling indicates one or more subsets of user equipment beams for at least two predefined subsets of uplink data from all possible user equipment beams.

21. The method according to claim 20, wherein:

22. The method of claim 18, wherein the method is performed by a user equipment and the downlink trigger signaling is scrambled with a scrambling identity assigned to the user equipment.

23. The method according to any of claims 18 to 22, wherein the predefined uplink signaling comprises uplink beam-reference signals.

24. The method according to any of claims 18 to 22, wherein the predefined uplink signaling is sent in predefined subframes and multiplexed with predefined uplink signaling from a plurality of other user equipments that are similarly triggered to send respective predefined uplink signaling.

25. The method according to any of claims 18 to 22, wherein the method is performed by a user equipment operating with a 5G mmWave radio access technology.

26. A computer readable storage medium having stored thereon program code configured to, when executed, cause a user equipment to perform the method of any of claims 18 to 22.

27. An apparatus for communication, comprising:

uplink data is transmitted on the identified one or more of the uplink beams.

28. The apparatus of claim 27, wherein the downlink trigger signaling is received after the apparatus transmits uplink data selected according to a basic uplink beam selection protocol that includes reciprocity, wherein a user equipment beam for uplink data is selected based on a network beam for downlink data.

29. The apparatus of claim 27, wherein the downlink trigger signaling indicates one or more subsets of user equipment beams for at least two predefined subsets of uplink data from all possible user equipment beams.

30. The apparatus of claim 29, wherein:

31. The apparatus of claim 27, wherein the apparatus is a user equipment and the downlink trigger signaling is scrambled with a scrambling identity assigned to the user equipment.

32. The apparatus according to any of claims 27 to 31, wherein the predefined uplink signaling comprises uplink beam-reference signals.

33. The apparatus according to any of claims 27 to 31, wherein the predefined uplink signaling is sent in predefined subframes and multiplexed with predefined uplink signaling from a plurality of other user equipments, which are also similarly triggered to send respective predefined uplink signaling.

34. The apparatus according to any of claims 27 to 31, wherein the apparatus is a user equipment operating with a 5G mmWave radio access technology.

35. An apparatus for communication, comprising:

means for invoking transmission of downlink trigger signaling to a user equipment, the downlink trigger signaling indicating a set of uplink beams;

means for receiving predefined uplink signaling using the uplink beam indicated by the downlink trigger signaling;

means for transmitting an acknowledgement to the predefined uplink signaling, wherein the acknowledgement identifies one or more of the uplink beams for use by the user equipment in transmitting uplink data; and

means for receiving the uplink data on the identified one or more of the uplink beams.

36. An apparatus for communication, comprising:

means for transmitting predefined uplink signaling with a set of uplink beams indicated by downlink trigger signaling in response to receiving the downlink trigger signaling invoked from a base station;

Means for receiving an acknowledgement to the predefined uplink signaling, wherein the acknowledgement identifies one or more of the uplink beams; and

means for transmitting uplink data on the identified one or more uplink beams.